Biological CorrelationsâThe Hansch Approach - ACS Publications

13 The Effect of a Penetrant Aid on Pre -Emergence Herbicidal Activity of Trifluoromethanesulfonanilides

Downloaded by UNIV LAVAL on July 11, 2016 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1972-0114.ch013

WADE VAN VALKENBURG and ANTHONY F. YAPEL, JR. 3M Company, St. Paul Minnesota 55133

Meta and para monosubstituted trifluoromethanesulfonani lides were tested for pre-emergence herbicidal activity against Foxtail and Wild Mustard. Activity was determined in the presence and absence of 0.1% by weight of a sur factant penetrant aid (Tween 80). The surfactant enhanced biological activity in some series members and reduced it in others. The change in biological activity caused by the surfactantwasrelated primarily to the change in octanol/ water partition coefficient induced by the surfactant. For para-substituted series members this change in partition coefficient was strongly correlated with variations in the Hammett sigma constant.

O u r f ace-active agents ^

(also k n o w n as surfactants, w e t t i n g agents, a d -

juvants, a n d spreader-stickers ) are c a p a b l e o f m o d i f y i n g t h e o b s e r v e d

biological activity of a herbicide.

Jansen et al. ( I ) tested t h e f o l i a r

a c t i v i t y o f three h e r b i c i d e s i n c o m b i n a t i o n w i t h 6 3 different surfactants. S o m e o f these

surfactants

enhanced

biological activity while

others

decreased i t . B e c h e r a n d B e c h e r (2) m e a s u r e d t h e s p r e a d i n g pressure, π, o f a series o f surfactants o n p l a n t a n d s y n t h e t i c surfaces.

T h e surfactants

were characterized b y H L B (hydrophile-lipophile balance) s i m i l a r to those o f Jansen's adjuvants.

values ( 3 )

T h e relationship between the

s p r e a d i n g pressure a n d t h e contact a n g l e c a n b e expressed as π = JL cos 0, w h e r e y

L

is t h e surface tension o f t h e l i q u i d a n d θ is t h e contact angle

b e t w e e n t h e l i q u i d a n d a s o l i d surface. B e c h e r a n d B e c h e r d e m o n s t r a t e d that surfactants i n t h e i r series w h i c h e x h i b i t e d m a x i m u m s p r e a d i n g pres252

Van Valkenburg; Biological Correlations—The Hansch Approach Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

13.

VAN VALKENBURG

AND YAPEL, J R

Herbicidal

253

Activity

sure c o r r e s p o n d e d q u i t e closely to those of J a n s e n s adjuvants of s i m i l a r H L B w h i c h o p t i m i z e d h e r b i c i d a l a c t i v i t y . I n d e e d , plots of either s p r e a d i n g pressure or Jansen's a c t i v i t y i n d e x vs. H L B y i e l d e d curves of s i m i l a r shape. F o y a n d S m i t h ( 4 ) r e c e n t l y r e v i e w e d the role of surfactants i n m o d i f y i n g the a c t i v i t y of h e r b i c i d a l sprays (66 references).

These

authors

s t u d i e d the a d j u v a n t effects of a surfactant b a s e d o n n o n y l p h e n o l w i t h v a r y i n g amounts of ethylene oxide a p p e n d e d .

A c t i v i t y was

enhanced

at a n o p t i m u m ethylene oxide c h a i n l e n g t h . T h i s is another w a y of s t a t i n g that there is a n o p t i m u m surfactant H L B for e n h a n c i n g h e r b i c i d a l ac t i v i t y o n a g i v e n species of w e e d . Downloaded by UNIV LAVAL on July 11, 2016 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1972-0114.ch013

T h e h y d r o p h i l e - l i p o p h i l e b a l a n c e is r e l a t e d to the s o l u b i l i t y of a surfactant.

A t h i g h H L B the surfactant is v e r y w a t e r s o l u b l e w h i l e at

l o w H L B the surfactant is v e r y l i p i d soluble. Because H L B is s o l u b i l i t y r e l a t e d , it is i n t u r n r e l a t e d to the p a r t i t i o n coefficient

( o r ratio of the

s o l u b i l i t y of the surfactant i n a l i p i d phase to its s o l u b i l i t y i n a n aqueous phase ). A h i g h H L B v a l u e suggests a l o w o i l / w a t e r p a r t i t i o n coefficient, and

conversely a l o w H L B shows a h i g h p a r t i t i o n coefficient.

Hence,

an o p t i m u m surfactant H L B for e n h a n c i n g b i o l o g i c a l a c t i v i t y also i m p l i e s a n o p t i m u m p a r t i t i o n coefficient for a c t i v i t y enhancement. H a n s c h a n d F u j i t a ( 5 ) h a v e p r o p o s e d a m o d e l for b i o l o g i c a l a c t i v i t y w h i c h m a y be expressed b y the f o l l o w i n g e q u a t i o n :

log ^ = ar} + where

br, +

pj +

rf

(1)

~ = log P - l o g P° Ρ = o c t a n o l / w a t e r p a r t i t i o n coefficient of a biologically active c o m p o u n d P° = p a r t i t i o n coefficient of a reference

compound

j = H a m m e t t sigma constant C = a c o n c e n t r a t i o n to y i e l d a g i v e n biological effect, often expressed as L D or L D 5 0

9 0

a, b, p, a n d rf are fitting parameters. The

H a n s c h e q u a t i o n m a t h e m a t i c a l l y describes

t r o l l i n g the b i o l o g i c a l a c t i v i t y of a c o m p o u n d .

two

events

con

T h e first i n v o l v e s c e l l or

m e m b r a n e p e n e t r a t i o n ( i n f l u e n c e d b y the p a r t i t i o n coefficient), a n d the second

i n v o l v e s i n t e r a c t i o n of the active m o l e c u l e

at a receptor

site

( m o d i f i e d b y variations i n the H a m m e t t s i g m a c o n s t a n t ) . C o n c e r n i n g E q u a t i o n 1, t h e p r i n c i p a l effect of a d d i n g a w e t t i n g agent to a h e r b i c i d a l s o l u t i o n is to change the p a r t i t i o n coefficient of the


254

BIOLOGICAL CORRELATIONS

T H E HANSCH

APPROACH

h e r b i c i d e f r o m F to Ρ'. T h u s the b i o l o g i c a l a c t i v i t y of a h e r b i c i d a l s o l u t i o n c o n t a i n i n g a surfactant m a y b e r e p r e s e n t e d as

lo

s (ΤΎΓ) \

L

D

='^ Α

p,

- g °) + ' lQ

9 0 /

p

+

2

p'

h

+

Œ

p,

- s °) lo

p

(2)

d!

F o r this system the p a r t i t i o n coefficient of the p a r e n t c o m p o u n d i n the absence of surfactant is chosen as the reference state. a c t i v i t y is expressed as L D

9 0

Herbicidal

( or t h e c o n c e n t r a t i o n i n m o l e s / a c r e neces-

sary to c o n t r o l 9 0 % of t h e s p e c i e s ) . If E q u a t i o n 2 is s u b t r a c t e d f r o m E q u a t i o n 1, a c o m p l e x

equation


w i t h m a n y n o n f a c t o r a b l e terms results. F o r s i m p l i f i c a t i o n , let us assume t h a t the p h e n o m e n o l o g i c a l f o r m of E q u a t i o n s 1 a n d 2 c a n b e u s e d e m p i r i c a l l y to c h a r a c t e r i z e the c h a n g e i n L D of a surfactant to a h e r b i c i d a l system.

9 0

resulting from the addition

This empirical relationship can

be expressed as log ( ^ )

= A (log Ρ -

If we let χ = (log Ρ—log log

log Ργ

+ Β (log Ρ -

log Ρ') + C., +

D

Ρ') the a b o v e e q u a t i o n becomes = A\

+ B

X

+ Ca + D

(3)

E q u a t i o n 3 thus represents the c h a n g e i n b i o l o g i c a l a c t i v i t y of a g i v e n c o m p o u n d c a u s e d b y the presence of a surface-active agent. t h e r i g h t side of t h e e q u a t i o n is negative, a c t i v i t y is e n h a n c e d .

If

I f i t is

p o s i t i v e , a c t i v i t y is r e d u c e d . Materials and Methods T h e details of t h e e x p e r i m e n t a l p r o c e d u r e h a v e b e e n g i v e n i n the p r e c e d i n g c h a p t e r ( 6 ) a n d are o n l y s u m m a r i z e d here. Test Plants. Seeds of the grass G i a n t F o x t a i l (Setaria sp.) a n d the b r o a d l e a f W i l d M u s t a r d (Brassica kaber) w e r e p l a n t e d i n a m i x e d soil (7) a n d bottom-watered until emergence occurred. T o p watering was t h e n u s e d for the rest of the test. Pre-Emergence Studies. P r e - e m e r g e n c e h e r b i c i d a l e v a l u a t i o n s of the 15 t r i f l u o r o m e t h a n e s u l f o n a n i l i d e ( T F M S ) d e r i v a t i v e s l i s t e d i n T a b l e I w e r e c o n d u c t e d i n a n a r t i f i c i a l l y i l l u m i n a t e d greenhouse. E a c h of the c a n d i d a t e c o m p o u n d s was a p p l i e d to a p p r o p r i a t e l y s e e d e d s o i l samples as a n aqueous d r e n c h at three or f o u r dosage levels r a n g i n g f r o m 1.25 to 20 l b / a c r e . A l l drenches c o n t a i n e d 1 % acetone ( w / v ) to a i d d i s p e r s i o n of the h e r b i c i d e i n w a t e r . E m e r g e n c e a n d p l a n t v i g o r w e r e m e a s u r e d after a 21-day g r o w i n g p e r i o d . H e r b i c i d a l dosages w e r e c o n v e r t e d to a m o l e / a c r e c o n c e n t r a t i o n d e s i g n a t i o n for purposes of H a n s c h c o r r e l a t i o n .


13.

V A N VALKENBURG A N D YAPEL,

JR.

HerblCtdal

255

Activity

L D o a n d LD90 values w e r e o b t a i n e d for e a c h h e r b i c i d e f r o m l o g p r o b i t plots c o n s t r u c t e d f r o m a p p r o p r i a t e d o s e - r e s p o n s e d a t a . A s d i s cussed i n the p r e v i o u s c h a p t e r ( 6 ) , b o t h L D a n d LD90 values for m e m b e r s of the T F M S h e r b i c i d a l series w e r e separately c o r r e l a t e d w i t h ττ a n d σ u s i n g t h e H a n s c h e q u a t i o n a n d its v a r i o u s m o d i f i c a t i o n s p r e s e n t e d i n this w o r k . E x c e p t for o b v i o u s v a r i a t i o n s i n the π a n d σ p a r a m e t e r coefficients necessary to a c c o u n t for the fact that the L D values for a l l d e r i v a t i v e s are less t h a n t h e i r c o r r e s p o n d i n g L D values, the same o v e r - a l l conclusions w e r e p r e d i c t e d w h e t h e r L D or L D values were u s e d i n c a r r y i n g out the v a r i o u s structure—activity correlations. B e c a u s e the L D v a l u e is a m o r e m e a n i n g f u l d e s i g n a t i o n of a c t i v i t y t h a n the L D v a l u e i n h e r b i c i d a l studies, w e r e p o r t a l l c o r r e l a t i o n results a n d c o n c l u sions i n terms of L D . Surfactant. P o l y o x y e t h y l e n e ( 2 0 ) s o r b i t a n monooleate (also k n o w n as T w e e n 80, A t - P l u s 109, or P o l y s o r b a t e 80) w a s o b t a i n e d f r o m A t l a s C h e m i c a l I n d u s t r i e s a n d u s e d as r e c e i v e d . It w a s u s e d at the 0 . 1 % ( w / v ) c o n c e n t r a t i o n l e v e l i n a l l h e r b i c i d a l a c t i v i t y evaluations a n d p a r t i t i o n i n g studies r e q u i r i n g the use of surfactant. Partition Coefficient. P a r t i t i o n coefficients of the T F M S h e r b i c i d e s i n b o t h the presence a n d absence of surfactant w e r e d e t e r m i n e d b e t w e e n 1-octanol a n d p H 1.0 w a t e r ( m a d e a c i d b y a d d i t i o n of H C I O 4 ) b y u l t r a v i o l e t spectroscopy. T h e a b s o r p t i o n s p e c t r u m of T w e e n 80 d i d not interfere w i t h the spectra of the s u l f o n a n i l i d e s ( 6 ) . Hammett Sigma Constant. H a m m e t t s i g m a constants, w h i c h are a measure of the e l e c t r o n - d o n a t i n g a n d w i t h d r a w i n g c a p a b i l i t y of a r o m a t i c substituents, w e r e t a k e n f r o m t a b u l a t i o n s of Jaffe (8). 5

5 0

5 0

9 0

5 0

9 0

9 0

5 0


9 0

Results S t r u c t u r e - a c t i v i t y correlations w e r e c a r r i e d out u s i n g least-squares regression analysis t e c h n i q u e s

o n a n I B M 360 c o m p u t e r .

As i n the

a c c o m p a n y i n g p u b l i c a t i o n ( 6 ) , the d a t a i n T a b l e s I a n d I I w e r e

fitted

to E q u a t i o n 3 i n stepwise f a s h i o n . S t a n d a r d statistical tests w e r e c a r r i e d out at e a c h stage of

fitting

to d e t e r m i n e the o v e r - a l l goodness of fit of

the χ a n d σ d a t a to the various e q u a t i o n a l forms e x a m i n e d .

A s i n our

p r e v i o u s s t u d y ( β ) , the most s t a t i s t i c a l l y significant correlations w e r e a l w a y s o b t a i n e d w h e n a c t i v i t y d a t a for m e t a - s u b s t i t u t e d a n d p a r a - s u b s t i t u t e d T F M S h e r b i c i d e s w e r e d i v i d e d i n t o t w o discrete series a n d fitted separately. Correlation between σ and χ. P r e l i m i n a r y plots of the h e r b i c i d a l p a r t i t i o n i n g d a t a o b t a i n e d i n the presence a n d absence of T w e e n 80 i n d i c a t e d t h a t the s u r f a c t a n t - i n d u c e d c h a n g e i n p a r t i t i o n coefficient ( χ ) a n d the H a m m e t t s i g m a constant (σ—see T a b l e I )

w e r e not

independent

variables. A p a r t i c u l a r l y strong r e l a t i o n s h i p existed, for e x a m p l e , b e t w e e n the apara values c h a r a c t e r i z i n g the 4 - s u b s t i t u t e d T F M S c o m p o u n d s

and

χ. E m p i r i c a l l y c o r r e l a t i n g σ w i t h b o t h first- a n d second-order terms i n χ u s i n g stepwise regression m e t h o d s y i e l d e d the f o l l o w i n g equations the m e t a - a n d p a r a - s u b s t i t u t e d series m e m b e r s .


for

256

BIOLOGICAL

Only para-substituted

TFMS

CORRELATIONS

T H E HANSCH

series members

(n =

APPROACH

7):

* ara = 0.062 χ + 0.087 (±0.196) =

0.140

2

=

0.020

SE

=

±0.402

F

=

0.10

r r

1.661 χ - 3.024 χ + (±0.273) (±0.500)


spam =

2

1.228

(4b)

= 0.950

r r

Only meta-substituted

(4a)

2

P

2

= 0.903 ±0.141

SE

=

F

= 18.68

TFMS

series members

(η =

6):

vmeta = 0.063 χ + 0.282 (±0.172)

(5a)

2

=

0.179

=

0.032

SE

=

±0.246

F

=

r r

2

0.13

vmeta = 1.175 χ - 1.753 χ + 0.734 (±0.775) (±1.197)

(5b)

2

r r

F

2

=

0.660

=

0.436

=

±0.217

=

1.16

I n E q u a t i o n s 4 a n d 5, r is the m u l t i p l e c o r r e l a t i o n coefficient, r is 2

the " p e r c e n t c o r r e l a t i o n , " SE is the s t a n d a r d error of t h e e q u a t i o n (i.e., the error i n t h e c a l c u l a t e d σ values ), a n d F is the ratio of the m e a n s u m of error squares r e m o v e d b y regression to the m e a n s u m of squares of the error residuals not r e m o v e d b y regression. T h e F - v a l u e s w e r e r o u t i n e l y u s e d i n statistical tests to d e t e r m i n e the goodness of fit of the a b o v e a n d f o l l o w i n g e q u a t i o n s . T h e n u m b e r s i n parentheses b e n e a t h the fit p a r a m eters i n e a c h e q u a t i o n denote the s t a n d a r d error i n t h e r e s p e c t i v e p a -


13.

V A N VALKENBURG A N D YAPEL, J R .

257

Herbicidal Activity

rameters. T h e y c a n also be u s e d to j u d g e the goodness of fit of a p a r t i c u l a r e q u a t i o n to the e x p e r i m e n t a l d a t a . R e f e r r i n g to E q u a t i o n 4 b , i t is evident that there is a statistically significant p a r a b o l i c r e l a t i o n s h i p b e t w e e n σ α ραΤ

T F M S derivatives.

a n d χ for t h e 4-substituted

B o t h χ a n d χ terms are necessary i n the o p t i m u m 2

c o r r e l a t i o n e q u a t i o n , as e v i d e n c e d b y t h e fact that the percent

correla

t i o n ( r ) j u m p s f r o m 2 % i n E q u a t i o n 4 a to 9 0 % i n E q u a t i o n 4 b u p o n 2

stepwise a d d i t i o n of t h e l i n e a r t e r m i n χ. N o s i m p l e l i n e a r c o r r e l a t i o n == ο,χ +

b, f o r ex

a m p l e , w e r e even less statistically significant t h a n t h e p o o r l y

between a a

correlated

par

a n d χ was found.

F i t s of t h e f o r m σ

ρ α Γ α

s i n g l e - t e r m q u a d r a t i c r e l a t i o n s h i p of E q u a t i o n 4a. Downloaded by UNIV LAVAL on July 11, 2016 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1972-0114.ch013

A s w a s true f o r σ b e t w e e n a ta me

ρ α Γ α

, n o statistically significant l i n e a r r e l a t i o n s h i p

a n d χ was found.

Q u a d r a t i c relationships f o r a ta

similar

me

i n f o r m to t h e relationships of E q u a t i o n s 4 a a n d 4 b are presented i n E q u a t i o n s 5 a a n d 5 b for the m e t a - s u b s t i t u t e d T F M S derivatives.

Both

χ a n d χ terms are a g a i n necessary for o p t i m u m c o r r e l a t i o n a l t h o u g h t h e 2

final

correlation relationship i n E q u a t i o n 5b for

statistically significant ( r Equation 4b ( r =

2

=

a ta me

is n o t n e a r l y as

0.44) as the final r e l a t i o n s h i p for

0.90).

2

A l t h o u g h E q u a t i o n s 4 b a n d 5 b are difficult to interpret i n a m e c h a nistic sense, they d o suggest that the c h a n g e i n p a r t i t i o n coefficient (χ

=

l o g ? — l o g P ' ) to b e e x p e c t e d u p o n a d d i t i o n of 0 . 1 % T w e e n 80 to a h e r b i c i d a l T F M S f o r m u l a t i o n w i l l b e influenced at least to some extent b y three factors: ( 1 ) T h e nature of the substituent ( X ) i n t h e T F M S a r o m a t i c r i n g ( 2 ) T h e p o s i t i o n of s u b s t i t u t i o n ( m e t a or p a r a ) i n the a r o m a t i c r i n g ( 3 ) T h e electronegativity v a l u e of its H a m m e t t s i g m a

of t h e substituent

(as reflected

b y the

constant).

W i t h respect to t h e a b o v e , i t is n o t u n l i k e l y that the o c t a n o l / w a t e r p a r t i t i o n i n g b e h a v i o r of a l l T F M S series m e m b e r s is influenced b y t h e effects that t h e m e t a a n d p a r a r i n g substituents exert o n t h e a c i d i c ( pK

a

=

4.45) p a r e n t - N H S 0 C F 2

3

side c h a i n . B e c a u s e of t h e d i r e c t resonance

effects that they exert o n the - N H S 0 C F 2

ing

(positive

σ ) or e l e c t r o n - d o n a t i n g

3

side c h a i n , e l e c t r o n - w i t h d r a w

( n e g a t i v e σ ) groups s u b s t i t u t e d

i n t h e p a r a r i n g p o s i t i o n of t h e T F M S p a r e n t c o m p o u n d , f o r e x a m p l e , m i g h t b e e x p e c t e d to influence m u c h m o r e strongly t h e a c i d i t y ( a n d h e n c e the p a r t i t i o n i n g b e h a v i o r )

of t h e r e s u l t i n g T F M S d e r i v a t i v e t h a n

w o u l d b e t h e case f o r s i m i l a r l y s u b s t i t u t e d m e t a derivatives ( w h e r e o n l y i n d u c t i v e or field effects are p o s s i b l e ) . r e l a t i o n b e t w e e n σ α> ραΤ

F u r t h e r m o r e , the significant cor

χ , a n d χ i n E q u a t i o n 4 b strongly suggests that 2

these resonance effects present i n p a r a - s u b s t i t u t e d derivatives

probably

influence t h e n a t u r e o f t h e i n t e r a c t i o n ( m i c e l l e f o r m a t i o n , etc. ) b e t w e e n h e r b i c i d e a n d surfactant to a m u c h greater degree t h a n i n t h e case of


258


T H E HANSCH

APPROACH

m e t a - s u b s t i t u t e d T F M S d e r i v a t i v e s ( w h e r e the c o r r e l a t i o n b e t w e e n

a ta, me

χ , a n d χ is p o o r e r ) . 2

A s s h o w n b e l o w , T w e e n 80 a d d i t i o n to b o t h m e t a - a n d p a r a - s u b s t i tuted T F M S

c o m p o u n d s often

affects their h e r b i c i d a l a c t i v i t y .

surfactant-induced change i n activity (whether

This

l e a d i n g to u l t i m a t e e n

h a n c e m e n t or i n h i b i t i o n ) i n a l l cases d e p e n d s s i g n i f i c a n t l y o n the c h a n g e i n p a r t i t i o n coefficient tion.

( χ ) of the h e r b i c i d e p r o d u c e d b y surfactant a d d i

O b v i o u s l y , the a b i l i t y to p r e d i c t χ f r o m a s i m p l e k n o w l e d g e

the H a m m e t t σ constant

characterizing a particular T F M S

( w i t h o u t r e s o r t i n g to t i m e - c o n s u m i n g p a r t i t i o n i n g m e a s u r e m e n t s ) i n m a n y cases p r o v e advantageous.

of

derivative would

I n this c o n n e c t i o n , t h e statistically


significant E q u a t i o n 4 b c a n be r e a r r a n g e d a n d s o l v e d for χ u s i n g the q u a d r a t i c e q u a t i o n to o b t a i n the f o l l o w i n g χ ανα = 3.024 ±

Λ/9.145 -

Ρ

expression.

6.644 ( 1 . 2 2 8 — σ

ραΓα

)

3.322 (6) = 3.024 ±

Vb.986 +

6.644

σ

ρατα

3.322 E q u a t i o n 6 is v e r y u s e f u l for e s t i m a t i n g changes i n the p a r t i t i o n coeffi c i e n t as w e l l as changes i n the h e r b i c i d a l a c t i v i t y of T F M S c o m p o u n d s (see

para-substituted

p r o d u c e d w h e n 0 . 1 % T w e e n 80 is a d d e d

below)

to the h e r b i c i d a l f o r m u l a t i o n s .

A n expression analogous

to E q u a t i o n 6

c a n b e d e r i v e d f r o m E q u a t i o n 5 b for m e t a - s u b s t i t u t e d T F M S series m e m bers a l t h o u g h the p r e d i c t i v e u t i l i t y of this latter e q u a t i o n w i l l

obviously

b e l i m i t e d b y the lesser degree of c o r r e l a t i o n b e t w e e n a ta> χ , a n d χ. 2

me

Herbicidal A c t i v i t y Correlations.

Tables I a n d II give

ence h e r b i c i d a l a c t i v i t y a n d p a r t i t i o n coefficient presence of 0 . 1 % this study.

T w e e n 80 for the 15 T F M S c o m p o u n d

F o r reasons

discussed

previously

pre-emerg

d a t a g a t h e r e d i n the

(6),

evaluated i n

i n the

correlations

w h i c h f o l l o w , the H a m m e t t s i g m a constant was a s s u m e d to be r e l a t i v e l y unaffected b y the presence of the surfactant, so that the σ-values l i s t e d i n T a b l e s I a n d I I c o u l d b e u s e d to correlate d a t a o b t a i n e d b o t h i n the presence a n d absence of surfactant.

Pertinent herbicidal activity data

for the T F M S c o m p o u n d s a c t i n g o n F o x t a i l grass are presented i n T a b l e I. S i m i l a r d a t a for

the same c o m p o u n d s a c t i n g o n the b r o a d l e a f

Wild

M u s t a r d are t a b u l a t e d i n T a b l e I I . F o r reasons o u t l i n e d i n the p r e v i o u s c h a p t e r (6), w e r e separated

T F M S compounds

i n t o m e t a - a n d p a r a - s u b s t i t u t e d series m e m b e r s ,

s t r u c t u r e - a c t i v i t y d a t a for

each

S i n c e our p r e v i o u s analysis (6)

grouping

were correlated

i n d i c a t e d that t h e 3 - S C H - T F M S

4 - S C H - T F M S d e r i v a t i v e s w e r e p r o b a b l y o x i d i z e d in vivo to 3

i n g sulfoxide

and/or

sulfone

and

separately.

3

and

correspond

d e r i v a t i v e s , d a t a points for these


series

13.

V A N VALKENBURG

ANDYAPEL,

JR.

Herbicidal

259

Activity

Table I . Pre-Emergence Control of Foxtail by Trifluoromethanesulfonanilides NHS0 CF 2

3

X = LogVLog P ' a


Substituent, Χ 4 4 4 4 4 4 4 3 3 3 3 3 3 3 H

No Surfactant

CF Cl SCH C H F OCH S0 CH CF CI F SCH » COCH OH S0 CH 6

3

3

2

3

3

3

2

a b

10.6 8.15 5.10 40.0 10.1 23.0 2.64 21.5 14.4 18.2 2.06 12.4 204.0 1.17 12.7

—

3

6

Tween 80

9.70 6.40 5.10 82.0 8.0 58.5 2.42 15.0 7.8 8.35

3

3

0.1%

3

14.6 128.0 1.5 8.0

σ +0.551 +0.227 -0.047 -0.170 +0.062 -0.268 +0.728 +0.415 +0.373 +0.337 +0.144 +0.306 -0.002 +0.647 0.000

1.57 1.36 1.04 1.10 0.75 0.70 0.19 1.30

—

0.62 0.35 0.28 0.41 0.15 0.45

-

m +0.039 +0.105 0.000 -0.312 +0.101 -0.405 +0.038 +0.156 +0.266 +0.338

—

-0.071 +0.202 -0.108 +0.201

See Ref. 6 for absolute values of log Ρ and log P'. Omitted from correlations; see text and Ref. 6 for details.

m e m b e r s w e r e a g a i n o m i t t e d f r o m t h e i r respective g r o u p i n g s i n d e r i v i n g the final c o r r e l a t i o n equations.

C o m p u t e r i z e d regression analysis t e c h

niques w e r e u s e d i n the u s u a l m a n n e r to fit t h e T F M S s t r u c t u r e - a c t i v i t y d a t a i n the separate m e t a a n d p a r a groupings to E q u a t i o n 3.

During

the fitting p r o c e d u r e , χ , χ, a n d σ terms w e r e a d d e d i n stepwise f a s h i o n , 2

w i t h the o r d e r of i n c l u s i o n of these terms d e t e r m i n e d o n t h e basis of statistical F-tests. T h e stepwise equations r e s u l t i n g f r o m the regression analysis are l i s t e d b e l o w for b o t h F o x t a i l a n d W i l d M u s t a r d . Correlation

of Foxtail Activity

4-Substituted

TFMS

Data

derivatives

(n =

6):

l o g ( ^ 2 _ ) = 0.415σ - 0.151 \LD9o/ (±0.197) r r

2

=

0.726

SE =

=

0.527

F

=

±0.173 4.46


260


Table II.

T H E HANSCH APPROACH

Pre-Emergence Control of W i l d Mustard by Trifluoromethanesulfonanilides NHS0 CF 2

3

7. = Log PLog P' a


Substituent, X 4 4 4 4 4 4 4 3 3 3 3 3 3 3 H

CF CI SCH CH F OCH S0 CH CF CI F COCH OH SG CH SCH 3

3

6

3

3

2

3

3

2

3

3

3

6

b

a b

No Surfactant

0.1% Tween 80

3.35 1.36 42.0 18.9 1.85 35.6 31.6 6.15 5.20 5.55 24.3 46.2 17.4 9.5 4.6

2.64 1.35 25.2 10.5 2.31 80.5 79.0 1.95 5.20 4.67 33.0 32.9 26.8 17.2 6.4

1.57 1.36 1.04 1.10 0.75 0.70 0.19 1.30

—

0.62 0.28 0.41 0.15 0.35 0.45

log

(LD '\ W

\LD J m

+0.551 +0.227 -0.047 -0.170 +0.062 -0.268 +0.728 +0.415 +0.373 +0.337 +0.306 -0.002 +0.647 +0.144 0.000

-0.103 -0.003 -0.222 -0.255 +0.096 +0.354 +0.398 -0.499 0.000 -0.075 +0.133 -0.147 +0.188 +0.258 +0.143

See Ref. 6 for absolute values of log Ρ and log Ρ'. Omitted from correlations; see text and Ref. 6 for details.

( »A

log

LO

\LD o/

=

9

=

0.750

2

=

0.562

SE

=

±0.193

F

=

1.92

r r

log

/LD

9 0

\LD

'\

9 0

/

=

0.085 χ + 0.424 σ - 0.232 (±0.173) (( ± 0 . 2 1 9 )

- 2 . 1 2 2 χ + 3.944 χ + 1.542 σ (±0.506) (±0.922) (±0.280) 2

=

0.977

2

=

0.955

SE

=

±0.075

F

=

14.26

r r

χ««χ =

(7b)

- 1.751

+0.929


(7e)

13.

V A N VALKENBURG

3-Substituted

TFMS

derivatives

log ( ^ ) \LD o/ r

0.508

=

0.258

SE =

±0.188

2

F


LO

\LD o/ 9

=

0.413

(8b)

-

- 1 . 0 9 8 χ + 1.868 χ (±0.289) (±0.444) 2

=

0.954

=

0.910

SE =

±0.080

r

2

F

10.11

=

Xmax =

9

261

1.04

=

r

log Λ;^ Λ = \LDeo/

Activity

5):

=

r

( »A

(n =

= 0.212 χ (±0.207)

9

log

Herbicidal

AND YAPEL, JR.

+0.851

- 1 . 1 5 8 χ + 1.958 χ + 0 . 0 5 4 σ (±0.536) (±0.820) (±0.319) 2

=

0.955

=

0.912

SE =

±0.112

r r

2

F

=

0.453

(8c)

3.47

Xm« =

+0.845

C o m p a r i s o n of E q u a t i o n s 7a to 7c for the 4-substituted T F M S r i v a t i v e s a c t i n g o n F o x t a i l grass c l e a r l y demonstrates

de

that χ , χ, a n d σ 2

terms are a l l statistically significant i n the final c o r r e l a t i o n r e l a t i o n s h i p of E q u a t i o n 7c.

T h e " c h a n g e - i n - a c t i v i t y " surface represented b y E q u a

t i o n 7c exhibits a m a x i m u m at x

m(UD

=

+ 0 . 9 3 . T h i s m a x i m u m corresponds

to a r i d g e a l o n g the p a r a b o l i c l o g ( L D o ' / L D o ) e n v e l o p e a n d represents 9

9

the locus of 4-substituted T F M S c o m p o u n d s for w h i c h the a d d i t i o n of 0.1%

T w e e n 80 causes the greatest i n h i b i t o r y effects o n h e r b i c i d a l ac

t i v i t y a r i s i n g o n l y f r o m s u r f a c t a n t - i n d u c e d changes i n the p a r t i t i o n co efficient

(i.e., χ ) .

Substituting χ

Μαχ

=

+ 0 . 9 3 i n t o E q u a t i o n 4b one is

a b l e to estimate that a T F M S d e r i v a t i v e c o n t a i n i n g a p a r a - s u b s t i t u t e d side c h a i n c h a r a c t e r i z e d b y a H a m m e t t s i g m a constant of « lie o n or near the i n h i b i t o r y χ

ηιαχ

ridge.

—0.15 w o u l d

R e f e r r i n g b a c k to E q u a t i o n 7c,


262


however,

T H E HANSCH

w e note that a l t h o u g h s u r f a c t a n t - i n d u c e d changes

APPROACH

in log

Ρ

s h o u l d b e h i g h l y u n f a v o r a b l e f r o m a n a c t i v i t y s t a n d p o i n t for a T F M S d e r i v a t i v e c o n t a i n i n g a p a r a substituent w i t h σ

ρατα

=

—0.15, the fact that

the coefficient of σ i n E q u a t i o n 7c is p o s i t i v e also i m p l i e s that the o v e r - a l l a c t i v i t y of the h e r b i c i d e m i g h t s t i l l r e m a i n a c c e p t a b l e

because of

the

f a v o r a b l e negative c o n t r i b u t i o n of the σ t e r m to l o g ( L D 9 0 V L D 9 0 ) . S i m i l a r c o m p a r i s o n of E q u a t i o n s 8a to 8c for 3-substituted d e r i v a t i v e s a c t i n g o n F o x t a i l grass reveals that o n l y χ statistically significant as s h o w n i n E q u a t i o n 8b.

2

TFMS

a n d χ terms are

T h i s i m p l i e s t h a t for

m e t a - s u b s t i t u t e d d e r i v a t i v e s s u r f a c t a n t - i n d u c e d changes i n the p a r t i t i o n coefficient are p r i m a r i l y responsible for changes i n the h e r b i c i d a l a c t i v i t y


of the various series m e m b e r s .

T h e fact that the H a m m e t t s i g m a c o n

stant is p o o r l y c o r r e l a t e d w i t h s u r f a c t a n t - i n d u c e d changes i n h e r b i c i d a l a c t i v i t y for m e t a - s u b s t i t u t e d T F M S d e r i v a t i v e s b u t strongly c o r r e l a t e d w i t h s u r f a c t a n t - i n d u c e d a c t i v i t y v a r i a t i o n s for p a r a - s u b s t i t u t e d d e r i v a tives w o u l d a p p e a r to be p r e d i c t a b l e f r o m the relationships of E q u a t i o n s 4 b a n d 5b.

I n E q u a t i o n 5 b , for e x a m p l e , it was s h o w n that surfactant-

i n d u c e d changes i n l o g Ρ for m e t a series m e m b e r s are not s t r o n g l y de p e n d e n t o n the v a l u e of the H a m m e t t s i g m a constant.

Since h e r b i c i d a l

a c t i v i t y v a r i a t i o n s p r o d u c e d b y the a d d i t i o n of T w e e n 80 d e p e n d

pri

m a r i l y o n c o r r e s p o n d i n g p a r t i t i o n coefficient changes i n the 3-substituted T F M S series m e m b e r s , it f o l l o w s f r o m E q u a t i o n 5 b that one w o u l d h a v e expected little or no c o n t r i b u t i o n of the σ t e r m i n E q u a t i o n 3 to the regression r e l a t i o n s h i p for m e t a - T F M S c o m p o u n d s .

final

T h e essential absence

of surfactant effects o n σ for 3-substituted T F M S series m e m b e r s a c t i n g o n F o x t a i l c a n be r e a d i l y v i s u a l i z e d b y c o m p a r i n g F i g u r e s 2b a n d 2d i n the p r e v i o u s c h a p t e r Correlation

(6).

of Wild Mustard Activity

Data

P r o c e e d i n g i n a m a n n e r i d e n t i c a l to that o u t l i n e d a b o v e for F o x t a i l grass, the f o l l o w i n g stepwise regression r e l a t i o n s h i p s w e r e d e r i v e d for the b r o a d l e a f W i l d M u s t a r d . 4-Substituted

TFMS

derivatives

(n =

6): (9a)

(±0.155) r

0.795 0.633

SE F

±0.174 6.89


13.

V A N VALKENBURG A N D YAPEL, JR.

log 0^-) \LD

Herbicidal

Activity

= 0.207 χ - 0 . 7 7 6 χ + 0 . 5 8 7 / ( o.396) * (±0.726) 2

9 0

=

0.814

2

=

0.663

SE

=

±0.192

F

=

2.95

r

log Ι^ζ^Λ = 0.754 χ - 1.773 χ - 0.318 σ + 0.986 \ L D 9 o / (±1.526) (±2.784) (±0.845) 2


r

=

0.828

2

=

0.685

SE

=

±0.228

F

=

r

TFMS

derivatives

log ( ^ ) = \LD9o/

9 0

/

=

(n =

5):

- 0 . 5 7 2 χ + 0.236 (±0.108) 0.951

2

=

0.903

SE

=

±0.098

F

=

28.05

r

(9c)

1.45

=

r

log (^ζ^Λ \LD

(9b)

±

r

3-Substituted

263

- 0 . 5 6 9 χ + 0.280 σ + 0.137 (±0.084) (±0.164) r

=

0.980

r

2

=

0.961

SE

=

±0.076

F

==

24.48

log ( i i ^ S L ) = - 0 . 2 5 9 χ - 0.177 χ + 0.382 σ + 0.009 \LD / f±0.449) (±0.686) (±0.267) 2

9 0

r

=

0.985

r

2

=

0.971

SE

=

±0.094

F

=

10.99


(10a)

(10b)

(10c)

264


T H E HANSCH

W h e n E q u a t i o n s 9a to 9c for t h e 4-substituted T F M S

APPROACH

derivatives

a c t i n g o n W i l d M u s t a r d are c o m p a r e d , it is e v i d e n t o n the basis of the F - v a l u e s for each e q u a t i o n that o n l y a single t e r m i n χ is statistically significant a n d that E q u a t i o n 9a p r o v i d e s the best m a t h e m a t i c a l d e s c r i p t i o n of surfactant effects o n h e r b i c i d a l a c t i v i t y .

E s s e n t i a l l y the

same

c o n c l u s i o n holds true for the regression relationships i n E q u a t i o n s 10a to 10c for t h e 3-substituted T F M S c o m p o u n d s .

A g a i n , a single t e r m i n

χ (see

E q u a t i o n 10a) p r o v i d e s a 9 0 % c o r r e l a t i o n of the s t r u c t u r e - a c t i v i t y

data.

A t least to a first a p p r o x i m a t i o n , therefore, it w o u l d a p p e a r that

for b o t h m e t a - a n d p a r a - s u b s t i t u t e d T F M S c o m p o u n d s a c t i n g o n broadleaf

Wild

M u s t a r d , the o b s e r v e d

the

changes i n h e r b i c i d a l a c t i v i t y


c a u s e d b y T w e e n 80 a d d i t i o n to h e r b i c i d a l f o r m u l a t i o n s c a n be e x p l a i n e d i n terms of the c o r r e s p o n d i n g p a r t i t i o n coefficients

changes the surfactant induces

of the various derivatives.

i n the

E q u a t i o n s 9a a n d 10a

b o t h suggest that those T F M S derivatives e x p e r i e n c i n g the greatest crease i n o c t a n o l / w a t e r T w e e n 80 (χ =

p a r t i t i o n coefficient

i n the presence of

de

0.1%

[ l o g Ρ — l o g P ' ] large a n d p o s i t i v e ) w i l l also e x h i b i t

the greatest e n h a n c e m e n t i n h e r b i c i d a l a c t i v i t y w h e n surfactant is a d d e d . Discussion Surface-active

agents

various ways (β, 9 ) .

c a n alter the effectiveness

of

herbicides

in

B y l i m i t i n g a c t i v i t y evaluations to pre-emergence

studies, one c a n e l i m i n a t e s u c h difficult-to-control variables as b o u n c i n g , coverage, e v a p o r a t i o n , a n d w e t t i n g .

T h e h e r b i c i d a l system

examined

here consisted of a series of m e t a - a n d p a r a - s u b s t i t u t e d trifluoromethane sulfonanilide

(TFMS)

pre-emergence herbicides

whose

activity

e v a l u a t e d i n the presence a n d absence of a constant c o n c e n t r a t i o n w/v)

was

(0.1%

of the n o n i o n i c surfactant T w e e n 80. A d m i x t u r e of this penetrant

a i d w i t h the various m e m b e r s

of the T F M S

h e r b i c i d a l series l e d

to

e n h a n c e m e n t of a c t i v i t y i n some cases a n d i n h i b i t i o n of a c t i v i t y i n others (6).

S t i l l other series m e m b e r s w e r e r e l a t i v e l y unaffected b y surfactant

i n t h e i r a c t i v i t y t o w a r d s F o x t a i l grass a n d the b r o a d l e a f W i l d M u s t a r d (cf.

L D o a n d LD90' values i n T a b l e s I a n d I I ) . 9

A s j u d g e d f r o m o c t a n o l / w a t e r p a r t i t i o n i n g experiments i n the pres ence a n d absence of T w e e n 80, the p r i n c i p a l effect of a d d i n g surfactant to the T F M S h e r b i c i d e s at the 0 . 1 %

(w/v)

l e v e l w a s to alter t h e i r r e l a

t i v e solubilities i n the aqueous a n d l i p i d phases.

S i n c e the trifluoro

m e t h a n e s u l f o n a n i l i d e s are a l l q u i t e h y d r o p h o b i c , the a d d i t i o n of

Tween

80 i n every case i n c r e a s e d the w a t e r s o l u b i l i t y of the c o m p o u n d i n ques t i o n a n d h e n c e decreased its o c t a n o l / w a t e r p a r t i t i o n coefficient

(6).

W h e n the most statistically significant relationships d e r i v e d for the meta- and p a r a - T F M S herbicides acting on Foxtail and W i l d M u s t a r d


13.

VAN VALKENBURG AND YAPEL,

JR.

Herbicidal

265

Activity

are c o m p a r e d (i.e., E q u a t i o n s 7c, 8b, 9a, a n d 1 0 a ) , it is evident that h e r b i c i d a l a c t i v i t y variations ( w h e t h e r enhancement or i n h i b i t i o n ) caused b y T w e e n 80 a d d i t i o n c a n be t r a c e d almost entirely to c o r r e s p o n d i n g s u r f a c t a n t - i n d u c e d changes i n the l i p i d - w a t e r p a r t i t i o n i n g b e h a v i o r of the active c o m p o u n d s (i.e., variations i n χ = l o g Ρ — l o g P ' ) . T h i s is c e r t a i n l y true for m e t a a n d p a r a T F M S derivatives a c t i n g o n W i l d M u s t a r d (see E q u a t i o n s 9a a n d 10a) a n d for the m e t a T F M S h e r b i c i d e s a c t i n g o n F o x t a i l ( E q u a t i o n 8 b ) . I n fact, o n l y for the p a r a - s u b s t i t u t e d T F M S derivatives a c t i n g o n F o x t a i l ( E q u a t i o n 7c) does the H a m m e t t σ constant m a k e a significant a d d i t i o n a l c o n t r i b u t i o n to the o v e r - a l l corre l a t i o n r e l a t i o n s h i p . T h e fact that σ α a n d χ are also strongly correlated (see E q u a t i o n 4 b ) further illustrates the extreme i m p o r t a n c e of surfac t a n t - i n d u c e d effects o n the p a r t i t i o n coefficient of each T F M S c o m p o u n d i n d e t e r m i n i n g its u l t i m a t e h e r b i c i d a l a c t i v i t y . T h i s strong c o r r e l a t i o n between σ ( a n d to a lesser extent a ta) a n d χ u n f o r t u n a t e l y i m p l i e s , h o w e v e r , that these variables cannot be altered totally i n d e p e n d e n t l y of each other if attempts are m a d e to change T F M S h e r b i c i d a l a c t i v i t y b y surfactant a d d i t i o n a n d / o r substituent variations i n the parent m o l e c u l e . O n the other h a n d , the large positive v a l u e of the σ parameter coefficient i n E q u a t i o n 7c suggests that T F M S c o m p o u n d s substituted w i t h strongly e l e c t r o n - d o n a t i n g substituents (negative σ v a l u e s ) i n t h e p a r a a r o m a t i c r i n g p o s i t i o n w i l l e x h i b i t e n h a n c e d a c t i v i t y against F o x t a i l w h e n T w e e n 80 is a d d e d to the h e r b i c i d a l formulations at a constant concentration l e v e l (cf. i n T a b l e I, for example, 4 C H - T F M S (a = - 0 . 1 7 0 ) and 4 O C H 3 - T F M S (σ α — - 0 . 2 6 8 ) a c t i v i t y against F o x t a i l i n the presence a n d absence of surfactant.


ραΤ

me

ρ α Γ α

3

para

ραΤ

A l t h o u g h experiments i n this s t u d y w e r e c a r r i e d out at a single c o n c e n t r a t i o n l e v e l of a specific surfactant a n d as s u c h are l i m i t e d i n scope, it is interesting to speculate o n the i m p l i c a t i o n s of our results, p a r t i c u l a r l y i f w e extrapolate t h e m to situations w h e r e the c o n c e n t r a t i o n a n d t y p e of surfactant are v a r i e d . These speculations must, of course, be verified b y f u r t h e r e x p e r i m e n t a t i o n . I n this r e g a r d , Jansen (1) has suggested that t h r o u g h p r o p e r use of surfactants h e r b i c i d a l spray solutions c a n be t a i l o r e d to meet specific situations. Steffens a n d C a t h e y (10) have l i k e w i s e p o i n t e d out that for enhancement of h e r b i c i d a l a c t i v i t y b o t h the relative concentrations of the h e r b i c i d e a n d a n a d d e d surfactant are c r i t i c a l . O u r results t e n d to substantiate these earlier conclusions. T h e fact that l o g ( L D o ' / L D o ) i n E q u a t i o n 3 exhibits χ-dependencies w h i c h are different for F o x t a i l a n d W i l d M u s t a r d suggests the p o s s i b i l i t y of a l t e r i n g grass a n d b r o a d l e a f selectivity of the T F M S h e r b i c i d e s b y p r o p e r use a n d a p p l i c a t i o n of sur factants. C o n s i d e r i n g first the meta-substituted T F M S c o m p o u n d s , w e 9


9

266


T H E HANSCH

APPROACH

n o t e that i f one w i s h e d to increase b r o a d l e a f ( W i l d M u s t a r d ) selectivity o v e r grasses ( F o x t a i l ) , E q u a t i o n s 8 b a n d 10a suggest that this m i g h t b e a c h i e v e d b y a d d i n g a p a r t i c u l a r t y p e o r a m o u n t of surfactant u n t i l ( l o g Ρ — l o g Ρ') equals + 0 . 8 5 w h e r e m e t a - T F M S a c t i v i t y vs. F o x t a i l is m i n i m i z e d . I f one w i s h e d to increase grass c o n t r o l w h i l e decreasing a c t i v i t y against broadleafs,

E q u a t i o n s 8 b a n d 10a suggest that this m i g h t b e

a c h i e v e d b y a d d i n g a surfactant that increases t h e p a r t i t i o n of t h e m e t a - T F M S h e r b i c i d e s ( l o g F — l o g P' p o s i t i v e ) .

coefficient

E x t e n d i n g this

l i n e o f r e a s o n i n g t o t h e p a r a - T F M S h e r b i c i d e s , w e note that a n increase i n grass c o n t r o l over b r o a d l e a f w e e d c o n t r o l m i g h t b e o b t a i n e d b y i n creasing l o g Ρ t h r o u g h a p p r o p r i a t e surfactant a d d i t i o n s u c h that ( l o g Ρ Downloaded by UNIV LAVAL on July 11, 2016 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1972-0114.ch013

— l o g Ρ') is a p p r o x i m a t e l y e q u a l to —2.0 (cf. signs o f χ d e p e n d e n c i e s i n E q u a t i o n s 7 c a n d 9 a ) . I n c r e a s i n g l y selective c o n t r o l o f b r o a d l e a f w e e d s o v e r grasses

might i n turn b e achieved

b y m i n i m i z i n g grass

control

t h r o u g h a d d i t i o n of a surfactant that w o u l d adjust ( l o g Ρ — l o g Ρ') to +0.93.

A t this v a l u e o f χ, grass c o n t r o l is m i n i m i z e d , a n d b r o a d l e a f

c o n t r o l is about t h e same as i f n o surfactant w e r e a d d e d (cf. E q u a t i o n s 7c a n d 9 a ) . A s p o i n t e d o u t i n the previous c h a p t e r (6), o u r analysis has d e m o n strated that surfactant a d d i t i o n to h e r b i c i d a l f o r m u l a t i o n s c a n p r o d u c e a v a r i e t y o f a c t i v i t y - e n h a n c i n g a n d i n h i b i t o r y effects. T h e s e effects a p p e a r to b e caused p r i m a r i l y b y alterations i n t h e l i p i d - w a t e r p a r t i t i o n i n g b e h a v i o r o f t h e h e r b i c i d e s c a u s e d b y surfactant a d d i t i o n .

Indiscriminate

use o f surfactants as penetrant aids a n d f o r m u l a t i n g agents i n h e r b i c i d a l screening a n d field tests s h o u l d thus b e a v o i d e d .

H e r b i c i d a l evaluations

i n t h e presence a n d absence o f surfactant c o u p l e d w i t h regression a n a l yses o f t h e t y p e discussed i n this a n d t h e p r e v i o u s c h a p t e r (6) s h o u l d p r o v i d e v a l u a b l e clues r e g a r d i n g the most advantageous use o f surfactants i n e n h a n c i n g o v e r - a l l h e r b i c i d a l a c t i v i t y a n d selectivity.

Acknowledgments T h e authors a r e i n d e b t e d t o J . B e l i s l e f o r t h e p a r t i t i o n

coefficient

measurements a n d t o J . W a d d i n g t o n a n d D . P a u l y f o r t h e p r e - e m e r g e n c e h e r b i c i d a l a c t i v i t y evaluations.

Literature Cited 1. Jansen, L. L., Gentner, W. Α., Shaw, W. C., Weeds (1961) 9, 381. 2. Becher, P., Becher, D., ADVAN. CHEM. SER. (1969) 86, 15.

3. Becher, P., "Emulsions: Theory and Practice," 2nd ed., pp. 232, Reinhold, New York, 1965. 4. Foy, C. L., Smith, L. W., ADVAN. CHEM. SER. (1969) 86, 55.

5. Hansch, C., Fujita, T., J. Amer. Chem. Soc. (1964) 85, 1616.


13.

V A N VALKENBURG

AND YAPEL,

JR.

Herbicidal

Activity

267

6. Yapel, A. F., ADVAN. CHEM. SER. (1972) 114, 183.

7. Trepka, R., Harrington, J. K., Robertson, J. E., Waddington, J. T., J. Agr. Food Chem. (1970) 18, 1176. 8. Jaffe, H. H., Chem. Rev. (1953) 53, 191. 9. Holly, K., "The Physiology and Biochemistry of Herbicides," L. J. Audus, Ed., Academic, New York, 1964. 10. Steffens, G. L., Cathey, H. M., J. Agr. Food Chem. (1969) 17, 312. February 10, 1972.


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Biological CorrelationsâThe Hansch Approach - ACS Publications

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